Modern large communication systems provide for transmission of data over packet switched networks. Communication is frequently conducted according to the open systems interconnection basic reference (OSI) model, in which communication is thought of as a hierarchy of layers, from layer 7, the application layer, to layer 1, the physical layer. The application layer defines interfaces and services are provided to end user applications in order to organize data for communication, and the physical layer defines actual physical and electrical connections between devices and the communications over these connections. Of particular interest is layer 3, referred to as the network layer, which governs the management of routing and relaying through networks, from one network node to another. Data packets are organized and transmitted according to protocols defined by layer 2, the data link layer, over connections and using procedures defined by layer 1, the physical layer.
Layer 3 entities may direct data to multiple different nodes, with data traveling to different nodes over paths that involve the same physical connections. In addition, the same physical link may carry multiple data channels. Routing of messages occurs at level 3, and is accomplished by exchanges of information between level 3 entities, such as routers, and construction of routing paths by routers. Routing involves the definition and selection of pathways within and between systems, and systems maintain and distribute information identifying pathways and links. Routers within a system exchange information between one another, and routers at the edge of systems exchange information with routers at the edge of other systems, and this information is shared with routers within systems, so that each entity receiving data to be transmitted can construct proper routine segments so as to convey the information to its destination.
One important communication protocol is border gateway protocol (BGP), which is frequently used between autonomous systems and is therefore classified as an interautonomous system routing protocol. Border gateway protocol transmissions may be used to route data from a provider network to a customer network, such as from an internet service provider (ISP) to a customer virtual private network (VPN). A provider network will route a transmission to a customer network using BGP, and once the transmission has arrived at the customer network, it will be directed to its destination by elements of the customer network. When information transfer between systems fails, or when an autonomous system or elements thereof fail to implement BGP correctly, customers lose the ability to connect to some or all remote devices, because proper routing information is not supplied. For example, a customer virtual private network site may lose the ability to connect to addresses at other sites, or may lose connectivity to other services and networks. A customer is aware only that connectivity has been lost, and does not know whether the reason is a failure of a physical link, a failure of a remote system to which the customer is attempting to connect, or a routing failure, for example. A customer simply reports the failure to the service provider, which then endeavors to resolve the problem as quickly as possible.